Streptococcus mutans, etiologic agent of dental caries, is divided into 7 serotypes. We have isolated and characterized antigens possessing determinants for serotypes a,b,c, and e. Also, we have found that several strains induce, in rabbits, immunoglobulins able to react with human heart-tissue in vitro. Crude wall and membrane preparations from these organisms adsorb tissue-reactive antibodies from human acute rheumatic fever sera. Preliminary data indicate that S. mutans may contain heart-reactive antigens (HRA) in common with S. pyogenes, etiologic agent of rheumatic diseases. These findings warrant caution in the trial of proposed anti-caries vaccines. During the proposed renewal period, we plan to isolate from S. mutans the pertinent HRA's; and we shall purify and immunochemically characterize these common antigens. These studies are necessary so deleterious antigens may be removed from molecular vaccines proposed by various investigators. Also, we shall attempt to determine the ultrastructural localizations in tissue of antibody binding site(s). A new and sensitive technique for immunocytologic staining will be employed (horseradish peroxidase-antibody). The presence of common or distinct binding sites for the anti-streptococcal immunoglobulins (S. mutans vs. S. pyogenes) will be determined. Finally, the possible origin of binding sites will be studied as we attempt to link lipoteichoic acid-HRA complexes to membranes (erythrocyte).